On the subject of next generation radio access systems for the third generation mobile communication of mobile radio communication systems, discussions on LTE (Long Term Evolution) is in progress at 3GPP (3rd Generation Partnership Project).
In LTE, it is a precondition that frequency and time scheduling are performed in resource block (RB) or resource unit (RU) units.
FIG. 1 is a diagram depicting this frequency and time scheduling. The working band is divided into resource blocks, and the frequency is allocated to a plurality of user terminals, that is mobile terminals (UE: User Equipment).
The working band is also time-divided into sub-frames in the time axis direction, and frequency in resource block units is switched and allocated to a plurality of mobile terminals (UE).
This scheduling of allocation in sub-frame units in the frequency axis and time axis directions is performed by the base station.
Scheduling is normally performed based on channel quality information (CQI) in resource block (RB) or resource unit (RU) units.
CQI corresponds to signal-to-interference ratio (SIR), and SIR at the mobile terminal side is normally measured by monitoring the level of a common pilot, which is common to users, from the base station.
In the above mentioned LTE, common pilot channels are arranged in the frequency direction with intervals downlink (Non-patent Document 1).
FIG. 2 is a diagram depicting the example of arranging common pilot channels (PC) in the frequency direction with intervals, which is described in Non-patent Document 1.
Patent Document 1 proposes a structure of attaching common pilot symbols and a known series in each slot in order to enhance the SIR measurement accuracy, and a communication device at the reception side estimates the SIR using common pilot symbols and a known series in the received slot.
In the above mentioned mode shown in LTE, the pilot arrangement interval increases if the insertion interval of the pilot channels is very large, if the number of transmission antennas is high, or if the number of multiplexed users is high. Because of this, the number of common pilots to be arranged in a resource block and resource unit in specific units decreases.
Measurement of I (interference power) to measure SIR is normally expressed by Expression 1, and FIG. 3 shows a conceptual diagram of the measurement. Expression 1 determines the difference between the average value of the pilot levels before and after and the position of the pilot channel as the interference power.
                              I                      f            +            1                          =                              2            3                    ⁢                      ∑                          [                                                                                                                                                              p                          j                                                +                                                  p                                                      j                            +                            2                                                                                              2                                        -                                          p                                              j                        +                        1                                                                                                              2                            ]                                                          Expression        ⁢                                  ⁢        1            